As is known in the state of the art, one limitation to the life of a laser gyro is directly linked to the operating time of the cathode. This operating time is limited by the sputtering of the oxide layer deposited on the cathode. For one considered cathode geometry, the life is mainly dependent on the current density required of the cathode.
The main characteristics of a triaxial gyro will first be reviewed. The current configuration of such a gyro (FIG. 1) uses a system of plasma discharges which leaves from a single cathode (CA) and is then split by passing into three linking capillaries (C1 to C3) which arrive at the gas reserves, respectively referenced B, C, D. To simplify the drawing of FIGS. 1 to 4, the cathodes are not represented, but the start of the corresponding capillaries linking to these cathodes. From each gas reserve there then leave two plasma conduction capillaries which supply the anodes. To simplify the drawing, FIG. 2 shows only the case of the gas reserve for the mirror D, the configuration of the elements relating to the other gas reserves being the same as for D. This reserve is linked to the anodes A1 and A2 by the capillaries CD1 and CD2, respectively forming part of the cavities defined by the mirrors (A, D, B, F) and (F, C, D, E) and by the capillaries linking them. The cathode CA is therefore linked to the six anodes (A1 to A6). This architecture makes it possible to keep a symmetrical configuration which uses two anodes for each cavity.
A triaxial laser gyro of the prior art, as mentioned above, for example the PIXYZ® gyro, has the following characteristics:                Triaxial laser gyro comprising three laser cavities, orthogonal to each other in pairs (see FIGS. 1 and 2). The three cavities are incorporated in one and the same block of Zérodur® characterized by a very low thermal expansion.        The triaxial assembly comprises six mirrors (three transmission mirrors and three piezoelectric-mounted relocatable mirrors, hereinafter called “piezo mirrors”). Each mirror is common to two cavities.        The gain providing the laser effect is obtained by the electrical discharges into an He—Ne plasma between one cathode and several anodes (preferably six).        The optical block has associated with it an activation system placed on one of the “trisectrices” of the block (a trisectrix is defined as follows: if the six mirrors A to F were to be placed at the respective centers of the sides of a cube, each trisectrix would be an axis joining two opposite peaks of this cube). This mechanical system provides a way of overcoming the so-called “blind zone” effect.        
If we consider more particularly a cavity, the cavity is enclosed by four mirrors. Two are used as “piezo mirrors” (mirrors with servo-controlled position), which makes it possible to adjust the cavity-length to an integer number of wavelengths. The other two are partially reflecting mirrors. One of these mirrors carries a reading system which, after the two beams CW and CCW (contrapropagative beams) from the laser cavity are recombined, makes it possible to obtain an interference pattern. If the cavity is rotating, this pattern passes in front of two photoelectric cells arranged in phase quadrature. The frequency seen by the cells depends on the angular speed of the optical block about the sensitive axis of the cavity. The phase between the two signals received by the cells depends on the direction of rotation of the cavity.
A diaphragm makes it possible to select the main mode TEM00 of the laser and reject the higher modes. One diaphragm is used for each cavity.
As described in French patent 2 759 160, optimizing the performance characteristics of the gyro entails more particularly:                The use of two electrical discharges for each cavity. Each discharge is established between the common cathode and an anode. The two anodes are placed in the plane of the cavity. This symmetrical definition makes it possible to overcome the gas flow effects in the cavity (Fizeau effect).        The use of an activation, the sensitive axis of which is combined with the “Cathode” axis (axis 1 passing through the cathode CA in FIG. 1).        The placement of this activation axis vertically in the carrier to make the thermal dissipation of the block symmetrical.        The use of balancing capillaries between the anodes to reduce the gyro power-up effects (see French patent application 95 01645).        
In a triaxial gyro as described above, the current required of the cathode is six times the operating current of the gyro. For an application requiring a very long life, this configuration is limited by the fact of the high current density required of the cathode, as specified above.